Apparatus for electrolytically treating metallic articles



Feb. 18, 1941. G. J. BECKWITH 2,232,019

I APPARATUS FOR ELECTROLYTICALLY TREATING METALLIC ARTICLES Filed July21, 1957 2 Sheets-Sheet 1 .fii... 1H v1.

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APPARATUS FOR ELECTROLYTICALLY TREATING METALLIC ARTICLES Filed July 21.1937 v 2 Sheets-Sheet. 2

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Patented Feb. 18, 1941 UNITED STATES APPARATUS FOR ELECTROLYTICALLYTREATING METALLIC ARTICLES Glenwood J. Beckwith, Brecksville, Ohio,assignor to The American Steel and Wire Company of New Jersey, acorporation of New Jersey Application July 21, 1937, Serial No. 154,913

3 Claims.

This invention relates generally to the electroly-tic treatment ofmetallic articles, and is particularly concerned with devices, andmethods of operating the same, for electrolytically coating a sucharticles in an improved manner.

There are two major problems encountered in coating metals byelectrolytic process in accordance with current practices. The first ofthese relates to the uneven distribution of the coating upon thesuperficial areas of the work-piece. The second relates to thedisfiguration of the coating during the plating operation. Each of theseproblems will be discussed briefly to afford better understanding of thepresent invention.

" It'is generally known that the amount of metal which iselectrodeposited on a given surface is proportional to the amount ofcurrent flowing. It is also known that when current is passed through asingle metallic conductor that flux 20 lines are set up around theconductor. These lines of force are generally known to encircle theconductor amuming the shape of the latter. In any electrolytic unitwheredirect current is em ployed it is commonly known that the current inpassing from the anode to the cathode tends to seek the shortestdistance and the sharpest edges.

The former tendency, however, is greatly diminished by the latter as inmost cases current will be attracted to a sharp point or a series ofpoints;

0 namely, a square edge rather than to afiat surface, even though theformer may be at a greater distance than the latter, Where flat strip isbeing electrolytically treated and electrodes of the parallel type arebeing used, the greater current 35 density, therefore, tends to exist atthe square edges of the metallic strip being treated. Hence, otherfactors being constant, metallic articles; such as, steel strips orsheets, which are electroplated in a continuous manner, inherently have40 heavier deposits near or on their edges than at their centers.

Many ideas have been tried in seeking to overcome this unevendistribution of the coating, among which will be found the provision ofellip- 45 tic'al anodes to increase the current density adjacent thecentral portions of the articles to be coated. Shielding for anodes on,or adjacent, their outer portions has been suggested, including the useof rubber bands, or other non-conductive 50 baffles, to diminish thecurrent density at the edges of the articles being coated. Any and allof the above means for correcting the uneven distribution of the coatinghave been found to be cumbersome and unreliable.

55 In connection with the second problem, the

troubles may be confined, generally speaking, to the contacts wherebythe negative or cathodic side of the circuit is introduced to thearticles to be coated. Such contacts may be divided into two groups: (1)those arranged to contact the work-piece beneath the surface of theelectrolyte, hereinafter referred to as internal contacts, and (2) thosearranged to contact the work exteriorly of the electrolyte, hereinafterreferred to as external contacts.

In the case of internal contacts, these, being the cathodes in platingoperations, are given to coating in the same manner as the work-piecesare coated. The accumulation of such coating necessitates frequentlyshutting down the apparatus to permit the cleansing or replacement ofthe cathodes.

Chain contacts, which are frequently employed internally of theelectrolytic bath, due to the fact that they present such a smallsurface for plating current of relatively high density, quickly acquiredendritic deposits of granular metal, which ultimately tend to drop uponthe articles being coated and become welded thereto and plated over,Undesirable surface imperfections on the finished articles are thuscreated. Furthermore, chain contacts are inclined to become stiff, dueto the metal deposited on them, and thereafter tend to scratch and marthe surface of the articles, resulting in surface imperfections on thefinal product that are highly objectionable.

Where rolls are employed as internal contacts, excessive deposits formquickly thereon and, particularly, on that portion of the rolls thatfalls between the paths of the articles being coated; such, forinstance, as in the case of strip, where annular deposits collectbetween strips. Such formations tend to bend the edges of the stripspassing thereby, and to lump, and otherwise disfigure, the coaJtingsacquired thereon. Chrome plated rolls take on loose deposits whichunravel and weld to the articles being coated. Contact bars scratch andspall small metal globules and require replacement, or not infrequentcleaning, of the cathode itself.

In the case of external cathodes, where rolls are employed forcontinuous plating operations, due to the fact that a certain amount ofthe electrolyte is entrained on the articles moving from the electrolyteto pass to the point of con- 0 tact with the cathode roll, such cathodesare also given to plating, which, for the reasons already enumerated, isregarded as highly objectionable. Such roll contacts, particularlywherein continu-- ous lengths of metal are being coated, are inclined toslip and scratch, or otherwise disflsure, the articles in contacttherewith.

In order to obviate such slipping. it has here-' tofore been proposed toemploy anti-frictional bearings for such cathode rolls, but ball orroller bearings, which are usually employed for this purpose, are soineiiiclent from the standpoint of electrical conduction, that it iscustomary to attention from time to time.

Where rolls are employed as internal contacts, the links are given toslight corrosion, whereby they become more resistant to the passage ofcurrent and, in some cases, become redhot and melt streaks in thecoating. Furthermore, the use of chain contacts greatly limits theextent of current density that can be used, and on high current densityoutput, the chains are of no use at all due to these overheatingeffects.

The present invention has for its principal object the provision of anovel method and apparatus for electrolytically coating metal whereinall of the objections and difficulties outlined above will be obviated.

More specifically, the invention has for its ob- Ject the provision ofmeans for electrolytically coating metallic articles, whereby arelatively uniform thickness of coating can be obtained on all coatedareas thereof. Another object is the provision of improved means forpreserving the finish and integrity of such coatings. Still anotherobject is the provision of improved methods for the electrolytictreatment of metallic articles, whereby the desired ends may be obtainedand the objectionable features of present day practices overcome. a

Otherobjects and advantagm will become apparent hereinafter by referenceto the following specification when read in conjunction with theaccompanying drawings, in which:

Figure 1 is a diagrammatic plan view of an electroplating apparatusembodying the invention.

Figure 2 is a longitudinal mid-sectional view of the layout shown inFigure 1.

Figure 3 is an enlarged fragmentary mid-sectional view showing a typicalarrangement of parts in the preferred embodiment of the invention shownin Figure 1.

Figure 4 is a sectional view taken along the line IV-IV in Figure 3.

Figure 5 is a fragmentary sectional elevational view illustratingcertain details of the invention.

Figure 6 is an end view of the construction shown in Figure 5.

These bus bars are supported and maintained in spaced relation by woodeninsulators 8. arranged in any desired manner.

Secured transversely of the vat I, and suitably mounted in anti-frictionbearings I arranged in spaced relation along the peripheral flange 3thereof, are pairs of rollers'l, each roller in each pair beingconstructed with ,a yieldable peripheral portion: such, for example. asa rubber covering and are pressed into engagement with each otherbybearing springs I3. Mounted adconductors I2, and anodic bus bars I inspaced relation. The cathode rolls are preferably chrome-plated copper,journaled in a plain bearing member II at each of their ends. Thebearing members II are preferably bronze, and of suflicient depth so asto engage the ends of the cathode rolls for a substantial distance alongtheir length, to afford good electrical contacts ofl'ering minimumresistance to the passage of current.

Carried at one or both ends of each of the cathode rolls I 0 is a beltI4, which extends to one of the adjacent pair of rubber covered rollers8. This belt may advantageously be made of rubber, and, when positionedas described, be under slight tension so as to insure that anyrotational movement of the pair of rubber covered rollers will betransmitted to the cathode rolls to rotate the same at a peripheralspeed corresponding to that of the rubber covered rollers.

Anodes I5 are disposed upon the bottom of the vat I intermediate thegroups of rubber covered rollers and cathode rolls, and are connected tothe positive bus bars 4 in any desired manner. It will be understoodthat for plating, the anodes carry the metal to be deposited. In thisconnection, it is customary in coating strip or sheet material toprovide another series of anodes substantially parallel to, butvertically spaced from those disposed on the bottom of the vat, so as toeffect simultaneous plating upon both sides of such strip or sheetmaterial, when it is passed therebetween.

In Figures 1, 2, 3 and 4, it is represented that a plurality of strips Sare being coated in accordance with the present invention and, thoughthe phases of the invention discussed hereinbefore are equallyapplicable .to the continuous plating of one or more strips or sheets ofany desired width, a plurality of strips has been adopted in order thatother phases of the invention (to be brought out hereinafter) may alsobe illustrated.

After passing through the necessary degreasers, scrubbers, and washers(not shown) the strips are introduced through the first pair of rubbercovered rolls 8; over the first cathode roll III, and downwardly intothe electrolyte solution I6, which is maintained at a level necessary tocover all anodes and articles to be coated in the coating process.

The strips are held beneath the electrolyte by suitable small rubbercovered sinker rolls ll, be-

tween which they extend in substantially flat coplanar relation,parallel to the faces of the anodes I5. They are then passed upwardlyout of the electrolyte to the next pair of rubber covered rolls 8, as isshown more in detail in Figure 3, where any electrolyte entrained on thestrips by the movement thereof is wiped off by the squeegee action ofthe rollers, which are set to squeeze the material passing therethrough.The strip thus wiped is passed on to the adjacent cathode roll, fromwhence it again is introduced into the electrolyte, in the manneralready described. Thereafter, the cycle is repeated until the stripfinally emerges through the last pair of rubber covered rolls 8, overthe final cathode roll Ill, and passes on to a take-up device (notshown) which advances all strips at the same rate of speed.

In the arrangement of the parts described above, it will be seen thatthe rubber covered rolls bear the tension and weight of the stripspassing through them, whereby the cathode rolls ID are held free of thisstrain, thereby permitting them to turn freely in the plain bearings I iwithout the aid of any anti-friction means. The rubber covered rollers 8are rendered adaptable for supporting the moving strips by theirrespective anti-friction bearings 1 whereby, notwithstanding the stressand strains to which they are subjected, they may rotate freely, andforward the stock by rolling it along without any slippage on thesurface thereof that causes disfigurement. In addition to this, the softyieidable surface of these rollers precludes any damage being doneto thecoating acquired by the strips.

The belts l4, transmitting the free motion of the pairs of rollers 8 totheir respective cathode rolls I0, insure that the latter willhavepositive rotation, and a peripheral speed corresponding to that ofthe stock, even though the cathode rolls are Journaled in plain bearingsfor the purpose of afiording the best possible electrical connectionwith the cathodic bus bars. The rotation of the cathode rolls in theirplain bearings H maintains the surface between the moving and stationaryparts clean and bright, thus assuring ample flow of the electriccurrent. The squeegee, or wiping action, of the rubber covered rollersinsures that any electrolyte entrained on the strips does not reach thecathode rolls, whereby the latter are maintained wholly free of anymetallic deposits, and the attendant disadvantages thereof areaccordingly obviated.

One of the greatest advantages to be derived from the relation of partsafforded by the construction of the present invention as shown herein,is that the cathode rolls III, in being adapted for the plating of aplurality of lengths of strip, or other flexible material, may beprovided with a series of annular fins l8, as are shown in Figure 4,which serve to space adjacent strips from each other, but which aresufficiently thin as to bring such strips into close edge-wiseproximity. This is desirable, since the field of magnetic fiux, whichsets up incident to the application of the electrolyzing current, andwhich is represented schematically in Figure '7 by arrows F, extendscompletely around the entire gang of strips, when arranged in thismanner, as though it were one piece; as is otherwise the case when eachstrip, having its own field of magnetic fiux independent of that of itsneighbor, (see Figure 8) is in substantially spaced or isolatedrelationship.

In the latter case, with the strips spaced apart, the action of the fiuxindicates that the current flows adjacent, or upon, the edges of eachstrip, thereby causing the greatest current density at these points, anda resultingly heavier local coating. However, when the strips are spacedclosely together so as to give a fiux field surrounding the entire bodyas a unit, as is shown in Figure 7, it is indicative that the greatatcurrent density occurs only at the exposed edges of the outermoststrips, where it tends to coat more heavily, but otherwise leaving allportions of the intermediate strips (including the edge portions)substantially uniformly coated. It will be understood that the fins I!are adjustably movable longitudinally of the cathode rolls toaccommodate any number of strips of any given width. In order that theoutermost strips may receive a uniform coating as well as those disposedintermediately thereof, it is proposed that an attractor wire I! bedisposed adjacent the exposed edge of each of the outermost strips (asis diagrammatically shown in Figure 1, and more clearly seen in Figure4) The attractor wires are to divert most of the current, inherentlyattracted to such exposed edges, away therefrom, so as to materiallydiminish the current density at these points, and thus to render theresulting coating of the same magnitude as that acquired on other areasof the outermost strips, and adjacent strips. The attractor wires I! maybe round, or any other shape, but preferably are flat (as shown) so asto provide corners or points to attract the current.

These wires may be run through the plating bath coextensively with, andparallel to, the strips, whereby they contact the cathode rolls andcarry the cathodic current in a manner similar to the latter, andreceive heavy deposits that would normally go to the exposed edgesthereof. These wires may be run through the apparatus in endlessfashion, or a new wire may be introduced by welding onto the recedingend of one then in the system. If the wires are re-used, they may, fromtime to time, be immersed in a molten bath of the plating metal in orderthat the accretion of coating can be recovered. It will also be apparentthat the outermost strips themselves may be utilized for attracting thedenser current, so that the intermediate strips will be uniformlycoated. It will also be apparent that bars parallel, and closelyadjacent, the path of the stock through the electrolyte, may be rigidlyset up and electrically connected with the cathodic circuit, wherebythey will serve to attract the denser currents, and thus hold theadjacent strips free from excessive deposits. Any suitable attractorarrangement is within the contemplation of the present invention.

From the foregoing it will be seen that the invention, as hereindisclosed, has overcome all of the disadvantages of conventionalapparatus enumerated in the forepart of this specification, in that anon-coating cathode is provided which cannot slip or stick, and yet,which is adapted to function efiiciently with currents of any densitywithout overheating. Also, the articles to be plated receivesubstantially uniform coatings, the finish and integrity of which arepreserved through the process.

Obviously, many changes may be made in the present construction which,though departing from the letter of this specification, will not bewithout the spirit of the invention: for instance, the spacer fins l8may be omitted where the stock to be coated is of sufilcient thicknessas to afford edgewise bearing for its several lengths upon themselves,or where the stock is otherwise susceptible of being controlled so as tomaintain the proximate relationship. The spacer fins are preferable,but. there are a number of ways of accomplishing this end, and anysuitable means is contemplated. Also, it will be understood that meansindependent of the squeegee rollers may that need driving to precludedamage upon the surface of the stock, are within the contemplation ofthe invention.

Therefore, while these modifications, and others too numerous tospecify, are not to be found specifically illustrated herein, it will beunderstood that they, nevertheless, fall within the purview of thepresent invention, as is more comprehensively set forth, and inaccordancewith, the appended claims.

I claim:

1. Apparatus for electrolytically metal strip or wire, including thecombination of a container for a liquid electrolyte, an electricalcontactor outside of the electrolyte containing portion of saidcontainer and means for tautly guiding strip or wire into and from saidcontainer and into engagement with said contactor, said means includinga roll over which said strip or wire passes and anti-friction bearingsjournaling the same, and said contactor comprising a metallic roller andplain bearings journaling the same, said means further including guideelements spaced on either side of said roll with at least one of saidelements at a lower level than said roll and said elements forming tautspans of strip or wire extending from said elements to said roll withone of said spans across said roller and the latter being positionedrespecting said roll and the one of said elements forming said spanacross said roller to effect deflection of strip or wire engaged by thelatter sufficiently to provide electrical contact with said strip orwire but insufllciently to cause the transmission to said roller ofmajor portions oi the strip or wire guiding stresses.

2. Apparatus for electrolytically treating metal strip or wire,including the combination of a container for a liquid electrolyte, anelectrical contactor outside of the electrolyte containing portion ofsaid container and means for tautly guiding strip or wire into and fromsaid portion of said'container and into engagement with said contactor,said means including pinch rolls between which the strip or wire passesand antifriction bearings journaling said pinch rolls, and saidcontactor comprising a metallic roller and plain bearings journaling thesame, said means treating further including a guide element forming ataut span oi strip or wire extending from said pinch rolls to saidelement across said roller and the latter being positioned respectingsaid pinch rolls and said element to eflect deflection of strip or wireforming said span sumciently to provide electrical contact with saidstrip or wire but insufliciently to cause the transmission to saidroller of major portions of the strip or wire guiding stresses, saidpinch rolls being positioned between said container and said contactorto engage strip or wire leaving said container and having rubber coveredsurfaces for engaging the strip or wire, the rubber covered surfaces ofsaid pinch rolls acting to remove liquid electrolyte from said strip orwire prior to its engaging said contactor.

3. Apparatus for electrolytically treating metal strip or wire,-including the combination of a container for a liquid electrolyte, anelectrical contactor outside of the electrolyte containing portion ofsaid container and means for tautly guiding strip or wire into and fromsaid portion of said container and into engagement with said contactor,said means including pinch rolls between which the strip or wire passesand antifriction bearings journaling said pinch rolls, and saidcontactor comprising a metallic roller and plain bearings journaling thesame, said means v further including a guide element forming a taut.span of strip or wire extending from said pinch rolls to said elementacross said roller and the latter being positioned respecting said pinchrolls and said element to effect deflection of strip or wire formingsaid span sumciently to provide electrical contact with said strip orwire but insuificiently to cause the transmission to said roller ofmajor portions of the strip or wire guiding stresses, said pinch rollsbeing positioned between said container and said contactor to engagestrip or wire leaving said container and having rubber covered surfacesfor engaging the strip or wire, said combination including means forrotatively interconnecting said pinch rolls and roller so that thelatter rotates with the former at synchronized peripheral speeds, therubber covered surfaces of said pinch rolls acting to remove liquidelectrolyte from said strip or wire prior to its engaging saidcontactor.

GLENWOOD J-. BECKWITH.

